Balancing arrangement for armature assemblies

ABSTRACT

A counterweight preformed from sheet stock is secured to the shaft of an armature at a selected angle of unbalance and correction plane by a press fit between the shaft and a hole in the counterweight.

United States Patent Stephen E. Smith lnventor Madison, Wis. Appl. No. 9,668 Filed Feb. 9, 1970 Patented Oct. 12, 1971 Assignee Giddings & Lewis, Inc.

Fond du Lac, Wis.

BALANCING ARRANGEMENT FOR ARMATURE ASSEMBLIES 5 Claims, 3 Drawing Figs.

U.S. Cl 74/573, 310/265 Int. Cl F161 15/22 Field of Search 3 10/265,

[56] References Cited UNITED STATES PATENTS 829,251 8/1906 Booraem 74/573 1,733,821 10/1929 Pontis 74/573 1,761,023 l/1927 Pontis 74/573 1,776,125 9/1928 Linn 74/573 3,141,485 7/1964 Bonner 1 74/573 3,377,846 4/1968 De Castelet 73/66 Primary Examiner-D. F. Duggan Assistant Examiner-R. Y. Skudy Att0rney--Harold E. Stohlgren ABSTRACT: A counterweight preformed from sheet stock is secured to the shaft of an armature at a selected angle of unbalance and correction plane by a press fit between the shaft and a hole in the counterweight.

PATENTED 0m 1 2197! TOHLGREN BALANCING ARRANGEMENT FOWARMATURE ASSEMBLIES This invention relates to'a means and method for correction of armature unbalance.

This invention is particularly suited to small armatures manufactured in large quantities for use. in small high-speed fractional horsepower motors such. as tised in household vacuum sweepers and hand-operated power tools. For purposes of this disclosure, the terms armature and rotor are used r han W t. v

Armature unbalance has in the past been corrected in a number of ways. For example, correction'weight has been added to selected armature core slots'in the form of measured lengths of wire. This method has the disadvantage that the armature slots often do not lie at the true angle of unbalance in which the weight should be added.- It is therefore sometimes necessary to divide the correction weight between slots on opposite sides of 'the true angle of unbalance location. This introduces additional steps in the application of the weights, complicates automatic assembly line balancing and increases the chances for errors. Another problem with such a method is that the wire may have substantial length so that the center ofmass of the wire cannot be located at theselected correction plane. This condition can cause correction plane crossover problems and inaccurate balancing.

In another prior method of balance correction, metal is removed from the armature body by drilling a series of holes or milling aseries of slots to predetermined dimensions A drawback with this method is that the area available for machining is usually limited because of the inherent design of armature slots. in addition, spacing of the armature slots requires compromise as to location of the correction. Metal chips from the machining operation can cause failure of the annature electricalcircuit." I

The present invention overcomes the above mentioned problems of balancing small armatures. Specifically, the invention provides a method and means by which unbalance of an armature or the like is correctedby securing a counter weight performed from sheet metal to one or each end of the armature shaft by a'press fit between the shaft and the hole in the counterweight.

In view of the foregoing, an object of the invention is to provide a rotor assembly in which unbalance correction is not complicated or limited by the design or configuration of the rotor.

Another object of the invention is'to provide a method of balancing rotor assemblies which is readily adaptable to automatic production of balanced rotors at minimum cost with a low percentage of rejects.

Another object of the invention is. to provide a weight for correcting unbalance in rotorassemblies which can be secured to the assembly with the centerof mass of the weight always located at the selected correction plane and angularly oriented to be at the angular location of unbalance.

Yet another object of the invention is to enable correction planes to be more widely separated in rotor assemblies, therefore gaining more balancing effect from the correction weight and enabling larger amounts of unbalance to be corrected. Referring to the drawings,

FIG. 1 is an elevation view of an armature or rotor incorporating the invention.

FIG. 2 is a section view along the lines 2-2 of FIG. 1.

FIG. 3 is a block diagram illustrating the several steps involved in a method of producing balanced armatures utilizing the improved armature unbalance correction method and means.

Measuring and correcting rotary machine parts for unbalance relative to their rotary axis is a highly developed art and is almost universally practiced whenever such parts are to be rotated at high speeds. Accurate balancing of motor armatures is essential to quiet and vibration-free motor operation. Small appliances such as household vacuum cleaners, power shop tools and the like all have high-speed electric motors. These motors may operate at a speed of 20,000 rpm. or more and an out-of-balance limit as small as 0.0009 oz.-in. is not uncommon.

Competition in the sale of armatures requires that the cost of each manufacturing step be kept to a very minimum. In one typical instance it was found that the cost of the armaturebalancing operation accounted for as much as 10 percent of the selling price of the armature unit. The present invention materially reduces this percentage by cutting the time for accomplishing the balancing operation and at the same time make. it possible to reduce balance tolerances and cut the number of rejected parts. 7

Referring to FIG. 1, the armature 10 comprises a cylindrical body 11 and a commutator l2 fixed to and adapted to be supported for rotation by shaft 13. The body 11 is formed with equally spaced axially aligned radial slots 14 which support multiple turns of insulated wire coils 15. The slots 14 may be skewed rather thanaxially aligned. The shaft 13 projects from opposite ends of the body forming relatively long cylindrical support-bearing surfaces 16 and 17 and short cylindrical surfaces 20 and 26.

The armature 10 has substantial length measured along the axis of its supporting shaft 13. Therefore, correction in two planes is required'to" dynamically balance the armature. According to standard practices these planes are arbitrarily selected. For best balancing results they should be widely spaced and lie near the ends of the body as represented by planes AA and BB'of FIG. 1. Planes AA and BB are perpendicular to the axis of rotation of the armature.

in accordance with the present invention, counterweights l8 and 19 are affixed directly to the shaft 13 and closely adjacent to the body 10 and commutator 12 at the location of plane AA and BB respectively. The counterweights l8 and 19 are preferably formed of strip sheet metal cut to length as will be further described below; in their preferred configuration each counterweight is formed with a hole 22 located near an edgesurface 23. The center of the hole and the center of mass M of the counterweight define an axis of symmetry XX of the counterweight.

The spacing between the hole 22 and edge surface 23 is preferably fixed while that of the opposite edge surface 24 is dependent upon the amount of correction required. The surfaces 23 and 24 are illustrated as being generally arcuate, however, they could just as well be squared. The counterweight 18 is retained on the shaft 13 at correction plane A-A by a press fit between the hole 22 and cylindrical surface 20. The counterweight is located axially on the shaft so that its center of mass M lies in plane AA. This location may, but not necessarily, be established by a shoulder surface 21 formed on the shaft.

counterweight 19 is formed similarly to counterweight l8 and is secured to the other end of the shaft 13 adjacent to the commutator 12. The cylindrical surface 26 engages the hole 22 with a press fit to locate the counterweight at the correction plane BB which may, but not necessarily, be established by shoulder 27.

The cylindrical surfaces of the shaft and hole in the counterweights by which each counterweight are joined to the shaft, as described above. allow universal radial orientation of the counterweight on the shaft. Thus, in accordance with one feature of the invention, the center of mass M of the counterweight 18 can be located at any radial angle of unbalance in correction plane AA as seen in FIG. 2. The center of mass M of the counterweight is located in opposition to the armature unbalance at plane'AA without limitations imposed by the design of the rotor. Likewise the counterweight 19 can be radially located to place its center of mass M at the angle of unbalance, not shown, associated with correction plane BB.

The above described counterweight device is particularly suited to automatic production line balancing of armatures. Unlike prior devices the center of mass M of the counterweights of the present invention will always be centered at their respective arbitrarily selected correction planes. The correction planes are widely spaced along the axis of rotation of the armature and the center of mass M of each counterweight can always be located in its selected plane of unbalance. As a result of the invention, it is possible to automatically balance armatures by the assembly line method with greater accuracy and speed.

Machines for measuring the amount and location of unbalance in rotating parts are well known in the art. Such machines are described in U.S. Pat. Nos. 2,243,379 and 2,944,424. The machine of U.S. Pat No. 2,243,379 is adapted to provide an electrical control signal representative of the amount of unbalance in either one of the two correction planes AA and BB in FIG. 1. The machine of U.S. Pat. No. 2,944,424 will locate the angle of unbalance for each of the correction planes and rotate the armature to orient the plane of unbalance to a fixed reference.

The armature-balancing means described above has particular application to a method of balancing armatures or similar rotating devices which represents one of the features of this invention. FIG. 3 is a schematic representation of a method of automatically balancing armatures utilizing the counterweight means described above. The individual items of equipment indicated at each station are well known in the art and any modification required to perform the present invention would be readily accomplished by one having ordinary skill in the art.

Block 30 represents a loading station from which armatures to be balanced are obtained. A transfer mechanism (not shown) serves to take armatures from the station 30 and to move them sequentially and in unison through each of the stations 31-35. Block 31' represents a balancing machine such as shown in the above mentioned U.S. Pat. No. 2,944,424. In its preferred form the invention contemplates a separate balancemeasuring machine for each of the correction planes AA and BB. After the armature has been transferred from station 30 to 31, the balance-checking machine is operated and develops a control signal representative of the amount of correction required at plane AA.

By way of a short review of the operation of the balancechecking machines of the above mentioned U.S. Pat. No. 2,243,379, the amiature is supported at its opposite ends for rotation in a pair of bearings carried by a cradle. The cradle in turn is supported with freedom to oscillate in a direction perpendicular to the axis of the armature and substantially in a horizontal plane. The armature is connected to a driving motor by a flexible drive which for example can be a belt or flexible coupling. Rotation of the armature by the drive motor will result in oscillation of the cradle due to rotor unbalance. A transducer connected to the cradle will generate a control signal which is a measure of the amount of unbalance correction required at a correction plane.

Simultaneously, with measuring the amount of unbalance, the same balancing machine locates the angle of unbalance for correction plane AA and rotates the armature to orient the angle to a known reference. U.S. Pat. No. 2,944,424 describes a control which serves to locate and orient the angle of unbalance. By way of a brief summary of the latter patent, a photoelectrically controlled mechanism coupled to one end of the armature serves to first locate the angle of unbalance and then to radially orient the armature with its angle of unbalance at a fixed reference.

During the next transfer operation the tested armature in station 31 is transferred to station 32 and the succeeding armature from station 30 is transferred to station 31. The transfer from station 31 to station 32 is made without disturbing the radial orientation of the armature. Station 32 includes a shearing and punching mechanism, not shown, for forming the counterweight 18 from a strip of rolled sheet material 32a.

Station 32 includes a measuring device adapted to play out a length of material 32a as controlled by the signal from station 31. A device adaptable to measuring a length of sheet material is described in U.S. Pat. No. 2,243,379. In this patent a signal such as the above mentioned first signal from station 31 serves to effect indexin of a cam which in turn acts as an abutment controlling the ength of travel of a hydraulic positioning cylinder. Station 32 also includes a mechanism, not shown, which serves to press the counterweight 18 into the shaft. During the pressing-on operation the counterweight is supported with its axis of symmetry XX in the angular location of unbalance and its center of mass M in opposition to the unbalance. The pressing operation places the counterweight at the correction plane AA as determined by. the shoulder 21 or by the stroke of the press mechanism.

From station 32 the armature is transferred to station 33 which comprises a measuring station like that of station 31. Here the amount of unbalance relative to correction plane BB is measured and its associated angle of unbalance is located. Again a control signal is generated representing the amount of unbalance and the armature is rotated to orient its angular location of unbalance to a known reference.

During the next transfer operation the armature is moved to correction station 34 where the counterweight 19 is applied to the shaft at correction plane BB. This step is identical to that of Station 32 previously described.

The next transfer is made to station 35 for final inspection of the armature balance at both correction planes. From station 35 the armature is transferred to a storage point or the start of another operation unrelated to the present invention.

With an armature located at each of the stations 31-35 and with simultaneous movement of the armatures between the stations, the output of completely balanced and inspected armatures is equal to one for each transfer increment.

1 claim as my invention:

1. An armature assembly supported for rotation about a central axis by a shaft projecting from opposite ends thereof, the assembly requiring unbalance correction in two selected axially spaced correction planes including, a cylindrical surface formed on each end of the shaft closely adjacent to the assembly, a counterweight supported on each of the cylindrical surfaces coincident with the angular locations of unbalance and the correction planes, each of the counterweights being a predetermined length of stock with a cylindrical hole near one edge and received on the cylindrical surface of the shaft with a press fit and having a center of mass radially spaced from the shaft a predetermined distance related to the amount of correction required.

2. An armature assembly according to claim 1 wherein the counterweight is formed from coiled sheet stock and is symmetrical with respect to an axis defined by the center of the hole and center of mass of the counterweight.

3. An armature assembly according to claim 1 wherein the shaft is formed with a radial shoulder at the inner end of each of the cylindrical surfaces to define predetermined correction planes by which the counterweight is located.

4. An armature assembly according to claim 1 wherein the center of mass of each of the counterweights is located in the angle of unbalance for the respective correction planes without limitations imposed by the assembly structure.

5. A counterweight for correcting unbalance in armatures by direct attachment to the armature shaft, the counterweight being formed of sheet metal including a cylindrical hole near one edge to receive the shaft with a press fit and a center of mass spaced from the hole, the center of the hole and center of mass defining an axis of symmetry of the counterweight. 

1. An armature assembly supported for rotation about a central axis by a shaft projecting from opposite ends thereof, the assembly requiring unbalance correction in two selected axially spaced correction planes including, a cylindrical surface formed on each end of the shaft closely adjacent to the assembly, a counterweight supported on each of the cylindrical surfaces coincident with the angular locations of unbalance and the correction planes, each of the counterweights being a predetermined length of stock with a cylindrical hole near one edge and received on the cylindrical surface of the shaft with a press fit and having a center of mass radially spaced from the shaft a predetermined distance related to the amount of correction required.
 2. An armature assembly according to claim 1 wherein the counterweight is formed from coiled sheet stock and is symmetrical with respect to an axis defined by the center of the hole and center of mass of the counterweight.
 3. An armature assembly according to claim 1 wherein the shaft is formed with a radial shoulder at the inner end of each of the cylindrical surfaces to define predetermined correction planes by which the counterweight is located.
 4. An armature assembly according to claim 1 wherein the center of mass of each of the counterweights is located in the angle of unbalance for the respective correction planes without limitations imposed by the assembly structure.
 5. A counterweight for correcting unbalance in armatures by direct attachment to the armature shaft, the counterweight being formed of sheet metal including a cylindrical hole near one edge to receive the shaft with a press fit and a center of mass spaced from the hole, the center of the hole and center of mass defining an axis of symmetry of the counterweight. 